Seeing an ad outdoors has a greater impact on us than one served to our laptop or phone. We come across it, 'discover it' if you want to be properly cheesy, we trust it more, and the creative is tied to a more unique and memorable set of circumstances.

This is of course debatable; there are lots of caveats, but I believe it to be true.

Bear with me on this post, there is going to be some pontificating on a Brian Cox-esque scale (for non UK readers, he's a TV broadcaster who gets very reflective about the universe).